Our long-term goal is to understand the detailed molecular mechanisms that control palate development (palatogenesis). Failure in palatogenesis results in cleft palate, which is one of the most common birth defects in humans. During the final phases of palatogenesis, the palatal periderm (a protective cell layer that prevents premature adhesion) must be removed in order for the medial edge epithelia (MEE) to properly adhere, which is prerequisite for establishment of the fused secondary palate. Previous studies have shown that transforming growth factor-?3 (TGF?3) plays an irreplaceable role in palate development, both in mice and humans, by regulating the fate of the MEE and adjacent periderm cells of fusing palatal shelves. Interestingly, truncated p63 (?Np63) protein levels are elevated in Tgfb3 knockout mice, while mice deficient in dNp63 or Irf6 are born with cleft palate resulting from the failure of the palatal epithelial cells to differentiate appropriately. Our recent data are the first to suggest that Tgfb3 is expressed in both the MEE and periderm and is necessary for periderm desquamation. Interestingly, p63 (?Np63) protein isoform levels are elevated in Tgfb3 knockout mice, while mice deficient in dNp63 or Irf6 are born with cleft palate resulting from the failure of the palatal epithelial cells to differentiate appropriately. Despite our advances, the mechanisms by which TGF?3 regulates palatal shelf adherence remain largely unknown, because the role of peridermal cells was not recognized, the genetic tools used to study palatal epithelial biology were not appropriate and technologies for direct real time observation of cell behaviors in the fusing palatal shelves were not available. Based on our preliminary and published data, we hypothesize that TGF?3 plays a cell-type autonomous role both in the periderm and underlying MEE, which is required to induce periderm desquamation during palatogenesis. The details of these mechanisms will be determined through execution of the following specific aims: in Aim 1 we propose to determine the cell-autonomous role of TGF?3 in palatal periderm removal during palatal epithelial fusion. In Aim 2 we will define the mechanisms, which regulate periderm generation and desquamation during palatogenesis, and in Aim 3 we will identify the mechanisms, by which the defective palatal shelf adhesion of Tgfb3-/- mice can be genetically rescued. Successful completion of the proposed experiments will identify mechanisms by which TGF?3 signaling controls palatal shelf adhesion and fusion; this knowledge may contribute in development of more advanced therapeutic strategies in the future.